1. Field of the Invention
The present invention relates to a power use circuit breaker and an electrical circuit arrangement for an electrical power generating plant using such power use circuit breaker.
2. Conventional Art
A power use circuit breaker, which interrupts a fault current flowing at a time of electric power system accident and protects the electric power system, is required to instantly interrupt a large fault current. In particular, a power use circuit breaker disposed between an electric power generator and a main power transformer, which is opened and closed at the time of starting and stopping of the electric power generator and further interrupts a large power generator fault current flowing at the time of accident, is required to have a capacity of interrupting a large current from several ten thousand to several hundred thousand amperes (A) containing a DC component.
A power use circuit breaker such as a puffer type gas circuit breaker and a vacuum circuit breaker which have been used to interrupt such large current has the following drawbacks.
(a) Puffer Type Gas Circuit Breaker
It is required a gas pressure of more than several hundred thousand atmospheric pressure which is to be blasted to a large current arc generated between contacts during current interruption to extinguish the arc for interrupting current of several ten thousand amperes, therefore, if a bellows having an operating stroke of 100˜300 mm in order to obtain the above high pressure gas, an operating force of about hundred thousand˜several tens of tons is required which increases the size of the machine.
(b) Vacuum Circuit Breaker
When interrupting a current containing a DC current component with a vacuum circuit breaker, it is impossible to attenuate the DC current component by making use of an arc resistance, because an arc voltage generated between contacts in the vacuum circuit breaker during current interruption is low, therefore, it is difficult to apply a vacuum circuit breaker for interrupting current in an electric power generator main circuit containing a large DC current component. Further, since a current conducting capacity of a vacuum circuit breaker is small, it is difficult to use a vacuum circuit breaker in a circuit in which current more than 4000 A flows.